Re: [Resend][Bug fix PATCH v5] Reusing a resource structure allocatedby bootmem

From: Yasuaki Ishimatsu
Date: Thu Apr 25 2013 - 21:58:16 EST

2013/04/25 5:37, Andrew Morton wrote:
On Wed, 24 Apr 2013 08:50:21 +0900 Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx> wrote:

When hot removing memory presented at boot time, following messages are shown:

[ 296.867031] ------------[ cut here ]------------
[ 296.922273] kernel BUG at mm/slub.c:3409!


The reason why the messages are shown is to release a resource structure,
allocated by bootmem, by kfree(). So when we release a resource structure,
we should check whether it is allocated by bootmem or not.

But even if we know a resource structure is allocated by bootmem, we cannot
release it since SLxB cannot treat it. So for reusing a resource structure,
this patch remembers it by using bootmem_resource as follows:

When releasing a resource structure by free_resource(), free_resource() checks
whether the resource structure is allocated by bootmem or not. If it is
allocated by bootmem, free_resource() adds it to bootmem_resource. If it is
not allocated by bootmem, free_resource() release it by kfree().

And when getting a new resource structure by get_resource(), get_resource()
checks whether bootmem_resource has released resource structures or not. If
there is a released resource structure, get_resource() returns it. If there is
not a releaed resource structure, get_resource() returns new resource structure
allocated by kzalloc().


Looks good to me.

--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -21,6 +21,7 @@
#include <linux/seq_file.h>
#include <linux/device.h>
#include <linux/pfn.h>
+#include <linux/mm.h>
#include <asm/io.h>

@@ -50,6 +51,14 @@ struct resource_constraint {

static DEFINE_RWLOCK(resource_lock);

+ * For memory hotplug, there is no way to free resource entries allocated
+ * by boot mem after the system is up. So for reusing the resource entry
+ * we need to remember the resource.
+ */
+static struct resource *bootmem_resource_free;
+static DEFINE_SPINLOCK(bootmem_resource_lock);
static void *r_next(struct seq_file *m, void *v, loff_t *pos)
struct resource *p = v;
@@ -151,6 +160,40 @@ __initcall(ioresources_init);

#endif /* CONFIG_PROC_FS */

+static void free_resource(struct resource *res)
+ if (!res)
+ return;
+ if (!PageSlab(virt_to_head_page(res))) {

Did you consider using a bit in resource.flags? There appear to be
four free ones left. The VM trickery will work OK I guess, but isn't
very "nice".

+ spin_lock(&bootmem_resource_lock);
+ res->sibling = bootmem_resource_free;
+ bootmem_resource_free = res;
+ spin_unlock(&bootmem_resource_lock);
+ } else {
+ kfree(res);
+ }
+static struct resource *get_resource(gfp_t flags)
+ struct resource *res = NULL;
+ spin_lock(&bootmem_resource_lock);
+ if (bootmem_resource_free) {
+ res = bootmem_resource_free;
+ bootmem_resource_free = res->sibling;
+ }
+ spin_unlock(&bootmem_resource_lock);
+ if (res)
+ memset(res, 0, sizeof(struct resource));
+ else
+ res = kzalloc(sizeof(struct resource), flags);
+ return res;

I think I'll rename this to alloc_resource(). In Linux "get" often
(but not always) means "take a reference on". So "get" pairs with
"put" and "alloc" pairs with "free".

I forgot to answer it.
I think so too. And I have no objection about your update patch.

Yasuaki Ishimatsu

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